Age-dependent variation of doubling times in malignant disorders: why are the doubling times of tumours in childhood shorter than in adulthood?

The proportion of patients with any given type of cancer in relation to all cases with malignant disorders in the same age-group exhibits a characteristic age-dependent variation. The values of age of maximal relative frequency (AMRF) were determined from statistics for seven cancer clusters grouped by target organ. The results of this study reveal that there exists a theoretical way of estimating AMRF by the linear combination of the approximative average values of tumour doubling times and the age of half-time development of the respective organ. The good correlation (corr. coeff. = 0.985, P < or = 0.001) between the observed and calculated values for AMRF makes the standard error of the calculation as low as 7.3 years. The conclusion is that in young developing organisms, only those tumours with short doubling time are likely to exist and survive, whereas later, during the period of organic involution and weakening cell-cell cooperation, more and more cancer types of longer doubling time can establish themselves. It seems that weak cellular cooperation yields way to malignancy; nevertheless, the normal growth rate of the target tissue has to be exceeded by the potential tumour. A slowly growing tumour in rapidly growing normal tissue is counterselected.